Follow the ranking criteria page to a tee, and take inspiration from mappers you enjoy. Focus on making it playable, and then add some flair to it. Have a lot of playtesters so they can give you advice on how to make it better, and take the advice seriously.
Finally, don't get overzealous. Don't go in trying to make "ThE nExT hArDeSt MaP iN tHe GaMe." Or breaking any boundaries and records. Remember, there's a reason why most people's first maps are tv size anime ops.
You might also want to make a spread of difficulties rather than just one, but that's up to you.
(Also keep in mind I've never uploaded any of my maps so take my advice with a grain of salt. I know a lot of this from creating things in other games and in life in general, but still just do what you want to do.)